1. Field of the Invention
This invention relates to a windowpane or windshield antenna, having a thin, electrically conductive layer flatly applied to an area of the windowpane, which is transparent to light, but reduces the transmission of heat.
In the invention, the conductive area is mounted on the windowpane, and is either directly applied to the window glass, or embedded between two layers of glass to form a composite or safety glass pane. A thin foil may serve as carrier of the conductive layer. This foil may be embedded between the glass panels of the composite or safety glass pane. When this layer is used as the main element of an antenna, it is desirable to use layers with the lowest possible surface resistivity. The lower the surface resistivity of the conductive areas formed by extremely thin metal and metal oxide layers, the higher the light-absorbing effect in the visible area. However, conductive layers with sufficiently high transparency cannot be realized with a surface resistivity of highly conductive materials such as copper or silver. These materials have a surface resistivity around 0.25 milliohm, which is lower by many orders of magnitude.
2. The Prior Art
Antennas of this type are preferably used in motor vehicle windshields where the conductive layer should be kept as transparent as possible. For this reason, the surface resistivity of the conductive layer must not be below 5 ohms. Antennas of this type are preferably used as radio reception antennas in the long, medium and short wave, VHF and UHF frequency ranges.
German Patent No. 37 21 934 A1 describes an antenna which uses a relatively low-resistive conductive layer. However, if antennas of the prior art are designed with layers of higher resistivity with better transparency, the antenna losses are relatively high, which results in comparatively low antenna capability. Such antenna losses have highly adverse effects, especially in the meter and decimeter (VHF) ranges.